Sound-radiating device



April 24, 1928 FL D. FAY ET Ai.,

SOUND RADIATING' DEVUJE Filed NOV. 20, 1925 2 .mirats-Sheet 3 R. D. FAY ET AL SOUND RADIATING DEVICE April 24, 1928.

Filed Nov. 2OJ 1925 2 Sheets-Sham 2 NJEIJ TERE- Il?? PS [SM- JW n n x WNV NYE Patented Apr. 24,- 1928.

UNITED STATES l1,667,251 PATENT ori-icaI RICHARD D. .'FAY, 0F CAMBRIDGE, .AND ROBERT E. BREWER, OF BOSTON, MASSA- CHUSETTS.-

SOUND -RADIATING DEVICE.

Original application led April 17, 1925, Seria1 No. 23,917. November 20, 1925. Serial No.

Our invention relates to an apparatus for radiating sound waves, and is adapted particularly` for use with radiophone receiving systems, although capable of more general 6 application and not limited to such use. 4

It is well known that electromagneticallyloperated sound-radiating devices commonly known as tloud speakers that employ diaphragms, sound chambers and horns are subject'to certain limitations chief of which is theirinability to reproduce the sounds initiated at the transmitting station without change of pitch and timbre or quality, the main cause of such distortion being the impossibility .of eliminating the natural period of the diaphragm and the stationary parts associated therewith. Another limitation to which such devices are subject is the absorption of energy by the stationary parts associated with the diaphragm or other vibrating member and the resulting creat/ion of mechanical vibrations in `such parts with the result that, for a given amount of received energy, the amplitude of the sound waves i emitted is reduced.

While loud speakers employing soundradiating members such as platesand cones constructed and arranged to propagate relatively-intense sound waves through the air are incertain respects more satisfactory than those of the diaphragm and horn type and reproduce sounds more faithfully over a somewhat wider range of frequencies, they do not, so far as we are advised,I overcome such objections as the undue amplication of sound waves havinf a pitch approximately equal to the naturalD period ofthe vibrating system, the wasting of energy by the creation of vibrations in parts intended to be 40 stationary, and the inability to -reproduce notes of .the lower frequencies unless the area of the radiating member is prohibi-' tively large. .A c The principal object of our invention, 4

paratus for the radiation of sound/waves of tofore been found possible without undulv increasin `sound-ra iating vmember' or members, the greatest linear dimension of our devicebelng only about one-,thirty-seventh' of the i wave length in -air of the lowest'toneto' be generically speaking, is to provide an ap-V the linear dimensions of the Divided and this application led 70,399.

reproduced, .and for the more` faithful and etiiclent reproductlon of the quality and pitch ofthe original sounds than canv be effected by the prior methods and apparatus.

Another object of our invention is to provide a sound-radiating device by means of which the sound waves produced bythe two surfaces of a sound-radiating member conof relatively intense sound waves `through the air will be prevented from interfering; or a sound-radiating device having twosuch sound-radiating members disposed oppositely by means of which duced by the inner surfaces of said members are prevented from interfering with those produced by the outer surfaces thereof.

Another object of our 'invention is to provide a sound-radiating device. in which the sound-radiating member is actuated by one of two oppositely-directed armatures each carried by a flexible supporting member together with means for preventing interference between the sound waves produced by the two'surfaces of said member; or a soundradiating devicey in disposed sound-radiating members are employed, each actuated by one of said armatures, together with means for preventing interference between'the sound waves pro` duced by the inner said radiating members. v

Various other objects of our invention will hereinafter'appear in the detailed description ofthe several illustrative embodiments of our invention.

ur invention contemplates the'use of two oppositely-disposed armaturessupported, respectively, by substantially-parallel flexible members, such asrelatively-stif discs', means for magnetizing saidfarmatures by variable electric currents-and a sound-radiating member constructed and arranged for the propagation of relatively intense sound waves through lthe air, as distinguishedfrom a telephone diaphragm or the like, "such soundradiating member, which may be plane, conical or -of any suitable configuration, being supported at its center or at its apex, as the case may be, on one of said armatures, together with means for preventing interference between the sound waves produced by the inner andv outer surfaces of said rathe sound waves pro-v which two oppositelyand outer surfaces ofv which permits the use of two oppositely-disposed sound-radiat- CII " of vsurfaces .where i form `a part oft is specication we members of any appropriate shape, conical or otherwise, each supportedv at its center on one of the armatures aforesaid, and

in the case of conical. radiating members,

each cone preferably flares' outwardly from'Y its point of support. In either'vcase we prefer to support the sound-radiating member solely by its actuating armatures.

Our invention comprises means whereby the sound waves produced by the two surfaces of a ,sound-radiating member constructed and arranged for the propagation of relatively intense sound waves through" the air will'be prevented from interfering. or means whereby the sound waves produced by the inner surfaces of two such'sound-radiating members oppositely disposed are prevented from interfering w'th the soun waves produced Vby the outer surfaces thereof, such means consisting in general of an enclosure screening two surfaces of a single sound-radiating member or the space between the two sets two oppositely-disposed members are employed.'

Our inventioncomprisesalso a sound-radiating device having 'two oppositely disposed sound-radiating members constructe andy arranged for the propagation through the air of .relatively intense sound waves o like'pressure phase together with means of anysuitable character for preventing inter'h ference Abetween the inner andouter surfaces of said members whereby we obtain areinforcing effect and a hemispherical, rather than spherical, sound wave distribution resulting in the doubling `of* the radiation'. resistance for each side halving ofthe areaA of each radiating member without reducing the radiation resistance. f

, Our invention comprises various parts and combinations of parts hereinafter more fully described and set 'forth inthe appended claims.

In the drawin s which accompanyv and shown in detail various embodiments of our invention which have given good results 1n practice and also several modiiications thereof; but theseconstructions are to be consid,- 5

ered as illustrative rather than restrictive, because the principle underlyingour. invention may be embodied iii a variety of apparatus.

on 'the line2--2 of In the',drawin Figure 1 is a front elevation of a sound-- radlating device embodying our` 1nvent1on;

- Fig. 2 isa vertical transversesection taken Fig. 1; `Fig.A 3 is a section onan corresponding to Fig. 2;

' 1 is a orizontal section of a' soundenlarged scale the space ybetween the' d but also tao hold said discs waves produced by the.

haveA indicated innig. 2

radiating device' in which only one radiating member is employed.

In the particular drawings selected for more fully disclosing the principle of; our invention 10 represents a permanent magnet having` two oppositely-disposed, .substantiallyv rigid arms shown bolted to a block which in turn is substantially-parallel flexible permeable ar mature-supportlng members 13, 13 which are shown in the resent "instance as relatively stijf, flexible d1scs,each clamped between va d pair of permeable rings 14,14 arranged on disc near the pethe opposite faces of each or bolts (not rphery thereof, by screws shown) In the present instance the discsv are secured to the permanent magnet by vboltsv 15 which assist in clamping the discs between their respective supporting rings. v

.The bolt 16 of non-permeable metal and ythe nuts 17 threaded -thereon,serve not only to clamp the discs between the rings `14, 14,

apart at their circumferences farthest away f from their points of attachment to qthe permanent magnet.

v'Iwo -oppositely-directed armatures 18 herein shown as tubular, are supported on said discs, respectively, at the centers thereof, 'and in the present ture is shown as having a threaded end projecting through its supporting disc, o n which ends nuts 19 are threaded to clamp the disc between said nut and a shoulder 20 on the armature.

" -It will be understood of 'course' that any -suitable means may be employed for securing said armatures to the discs.

,Supported by the armatures in any suitable manner `are oppositely-disposed soundradiating members 21, 22, which may be of parchment, bre, or any other suitable relatively-thin, stiff, homogeneous material, and preferably the vssaid sound-radiating members, if conical as shown herein, have their peripheral portions'slightly bent back, as shownat 23 to slightly stiifen the same near their peripheral edgesV and thereby vprevent substantial deformation thereof by giving said member-s relatively greater rigidity near tions, whereby therperiphery of each member is. substantially. free to vibrate with the same amplitude asv any'other portion. As` every element of the bent portionV 23 forms' with the plane of the base of the tympanum the same an veleircient of said tympanum.

rigidly s1. aced instance each armaat their central por' lll) le as every vla@ l sound-radiating member is supported solely7 to which the tympanum at its apex on its actuating armature by means ofa sleeve 24 which passes through the apex and is threaded to the outwardly projecting end of the armature, said sleeve being formed integral with a conical portion may be attached by gluing or otherwise. lVhen so supported, each sound-radiating member is free to vibrate substantially as a Whole. The said sleeve and conical member 25 or whatever other device is employed for coupling the tympanum to the armature, should be of wood, aluminum or other light material.

A magnetizing coil 26 is arranged in the space between the discs and is concentric with the armatures, said coil being wound on an insulating spool 27 supported in thepresent instance in the rabbeted inner peripheries of the adjacent rings 14. In order 'to avoid the possible detrimental effects vof air compression in the space between the spool and the discs, vided with a series of holes 28. The juxtaposed faces of the armatures which are separated by a relatively short gap are plane and are normal to the common axisof the two armatures so that they arein absolute parallelism, and in our preferred construction, the said armatures are slotted longitudinally to leliminate eddy current losses, as shown at 29. V

When the magnetizing coil 26 is energized b v current lmodified in accordance with sound waves' initiated at another point as for example the variable uni-directional currents in the plate circuit of a radiophone receiving system to which said coil is electrically connected, or by variable 'electric currents of any nature, the constantmagnetic flux 1n the air gap between the armatures created by the permanent magnet will be modified and hence the magnetic pull on the armatures will'be'changed, and as the same on each armature in opposite directions, the motions of said armatures will be equal and opposite, thereby causing the outer surfaces of the concs to produce sound waves of like pressure phase and the inner surfaces thereof to produce sound waves of like pressure phase opposite to that of the phase of the sounds produced by said outer surfaces. It will be noted that a force acting on any element of the system is balanced by an equal and opposite force on the counterpart of such element so that the tendency of the moving elements to create mechanical vibrations in their associated stationary parts is eliminated and practically all of the energy of motion is converted into sound waves.

those of the the inner rings 14 may be -prospace between the force acts Ths saving of energyis especially important in the reproduction of the lower fre- I quencies and we have succeeded by our invention in reproducing the lowest audible notes with substantially the same facility as upper register by using soundradiating cones whose diameter is about I twelve inches or approximately one thirtyseventh of the wave length in air of the sound made by the lower notes of a piano,

say, about thirtv cycles per second.

In order' to reproduce sounds of low pitch the radiating 'member must have a comparatively large areabecause the radiation depends on the square of the area or on the fourth power of the radius if the tympanum 'is circular,

when the radius of the surface is small with sound, provided however that the sound waves produced by the opposite surfaces of the sound-radiating member are prevented from interfering with each other. In the absence of such means for preventing interference practically no radiationcan be efthe radius is approximately a quarter wave-length of the sound, and in the present instance our sound-radiating members would have to be about 220 in diameter in order to radiate waves having a frequency of thirty per second unlesssuch interference was prevented.

` W' e therefore ing interference surfaces of the cones 21, 22, or 1n the case where a single cone or sound-radiating member of other shape is employed as illustrated in Fig. 4, means for preventing interference between the sound waves produced by the inner and outer surfaces of the single soundradiating member. Such prevention of interference may be accomplished in a variety of ways, and in the present instance we have illustrated the arrangement which we prefer to use for this purpose, viz., a. casing 12 -which sufficiently encloses and screens the inner surfaces of said members, or the inner surface of the memberi21-in Fig. 4, to prevent the sound waves produced `by said inner surfaces (or surface) from interfering with the sound waves produced by the outer surfaces (or surface) thereof, the said casing surrounding at least a portion of the convex side ofthe soundradiating member and substantially preventing interference .between the Asound waves emanating fromthe convex side and the concave side of said member or members.

Inasmuch as the outer surfaces of the cones create sound waves of like pressure phase and interference between said Waves and those produced by the inner surfaces is prevented, -we obtain substantially the same reinforcing effect as if a rigid medial pla-ne through which sound Waves could not pass were placed between the cones normal to the respect to the wave length of the provide means for preventbetween 'the'inner and outer clampedv to onev of v shown in Fig. 3

porting armature to its disc.

tures may be adjusted 'the free armature 1s armature whlch employed, or,

axis of the armatures, and also a hemispherical, rather than a spherical, 'soundwave distribution. which results in the doubling of vlthe radiation resistance for each side,-in other words, thearea of each surface may be halvedwithout reducing the radiation resistance.

i The length. of the gap between the armaby means of the screw 30 threaded into one of the 'arms of the magnet 10 and having its end bearing against the other.' f

Fig. 4 shows a sound-radiating device embodymg our invention that is particularly designed for incorporation in the cabinet o a'radio receiving set. In this construction found to react on the supports the sound-radiating member 21 and to reinforce its action. The nut 19 whereby the free armature is the discs 13 may be than the corresponding nut for securing the other arma.- ture'tov the other disc, if thelatter nut be as shown in Fig. 4, the threadto clamp the non-sup- Ineither case the weig t of said 'n ut on the free armature will serve in a certain degree to compensate for the reduction of weight resulting from the omission 'ofV the cone 21. There isevidently a vmagnetic coupling between the arslightly larger ed sleeve 24 may serve matures which tends to balance the two sides of the vibrating system.

Without limiting ourselves to any specific type of cone, or in fact to a sound-radiating member of any particular shape, we prefer to employ conical sound-radiating members capable of producing sound waveshaying Y.

wave fronts' which as claimed in our application Ser.

are initially, curvilinear No. 69,368,

tiled Nov. 16, 1925 as a division of our application, Ser. No. 23,917, filed Apr. 17 1925. This application i's a division of 'our ap? plication Ser. No. 23,917, tiled Apr.y 17, 1925.

Having thus described illustrative embodiments of our invention Without however members;

by Letters Pat-ent are bythe inner and vouter surfaces Iof said sound-radiating 2. In-a sound-radiating device, two oppositely-disposed sound-radiating members constructed and arranged for the propagation through' the air of relatively-intense sound waves of like pressure phase, and means sufficiently enclosing and screening the space between, the inner surfaces of said members to prevent interference between the soundwaves produced by the inner and outer v surfaces thereof.

-3. In a sound-radiating device, a free- 'edge conical tympan of relatively-thin, stiff, material having its peripheral portion n reversely bent to increase the peripheral ri `gidity thereof, every element of thebent portion of said tympanum orming'with the plane of the' base of said tympanum the same angle as every element of said tympanum. Y In testimony subscribed our-names( nlcmnnn'mr lBonner E. Blutvvnn.

November, 1925.

whereof, we have hereunto 

